The present invention relates to a degreasing apparatus and, more particularly, to an ultrasonic degreasing apparatus for degreasing parts for an electronic device and the like by using ultrasonic waves.
With the recent tendency to the total abolition of Freon and 1,1,1-trichloroethane which destroy the ozone layer, alternative methods and substitutes have been developed rapidly. Recently, in cleaning apparatuses, the use of degreasing methods using ultrasonic waves has increasingly been popularized. In these methods and similar methods, the following techniques have been proposed:
(1) techniques associated with plating apparatuses, in which objects to be processed are stored in a porous barrel and dipped in plating solutions (degreasing, pickling, plating, and cleaning solutions), and the barrel is rotated, with an ultrasonic oscillator being arranged in the apparatus, and more specifically, a technique associated with a plating apparatus, in which objects to be plated are stored in a porous barrel and is dipped in a plating solution together with the barrel, and ultrasonic waves from an ultrasonic oscillator are applied to the objects while the barrel is rotated, thereby efficiently plating the objects, as disclosed in Japanese Utility Model Laid-Open No. 61-103477, a technique of loading a barrel containing objects to be plated into a plating bath, and vibrating the plating bath with ultrasonic waves, as disclosed in Japanese Patent Laid-Open No. 59-74300, and a method of cleaning the aluminum tube of a photosensitive drum with an organic solvent, which method is designed to uniformly clean the entire surface of the aluminum tube by operating an ultrasonic oscillator while rotating the tube, as disclosed in Japanese Patent Laid-Open No. 58-108568;
(2) techniques without ultrasonic oscillators, such as a technique using mechanisms for raising/lowering and conveying a barrel and supplying a cleaning solution and a technique of cleaning objects to be processed by swinging the objects in a cleaning bath, and more specifically, a technique of cleaning plated objects in a barrel with water from a spray port together with the barrel, and cleaning a residual plating solution from the barrel and the objects, as disclosed in Japanese Patent Laid-Open No. 1-100300, a technique of cleaning a barrel containing objects in a degreasing bath and a pickling bath (in this technique, the barrel is rotated in each bath to allow efficient cleaning, and plating and cleaning operations are performed afterward), as disclosed in Japanese Patent Laid-Open No. 3-79792, and a technique associated with an apparatus for cleaning a shadow mask, in which an ultrasonic vibrator is arranged in a cleaning bath, together with a means for swinging the shadow mask in the cleaning bath, and the shadow mask is cleaned while the distance to the ultrasonic vibrator is changed, thereby uniformly cleaning the shadow mask; and
(3) techniques of performing a cleaning operation upon improving the cleaning efficiency of ultrasonic waves by deaeration (Japanese Patent Laid-Open Nos. 63-221878, 1-27680, 1-30686, 1-123683, and 4-207030).
Furthermore, with regards to hydro-extraction of process solutions, the following techniques have been proposed:
(4) a method of decreasing the amount of process solution carried away while objects to be processed are conveyed between solution baths (Japanese Patent Laid-Open No. 1-100300); and
(5) a method of performing sufficient hydro-extraction by holding a barrel, taken out from a process solution, above a bath for a long period of time according to a conveyance program.
Note that both methods (4) and (5) are designed to process objects which are easily deformed.
In the above conventional techniques, the types of process solutions are not limited, and process solutions suitable for the respective processes are used. As a factor indispensable for the alternative cleaning (degreasing) method described above, the use of water as a process solution is conceivable.
A conventional degreasing apparatus using water as a process solution will be described below with reference to FIG. 11. First of all, objects 1402 to be processed are stored in a barrel 1401 made of a porous wire mesh in the form of a hollow hexagonal column. The barrel 1401 is then loaded into a cleaning section 1403 filled with distilled water. The cleaning section 1403 is deaerated in advance by a first deaerating section 1409 using a vacuum pump 1411. The distilled water is circulating between the cleaning section 1403 and the first deaerating section 1409. When the barrel 1401 is loaded into the cleaning section 1403, an ultrasonic oscillator 1407 is started, and the barrel 1401 is rotated by a rotating means (not shown). When deaeration in the cleaning section 1403 is completed, the objects 1402 are loaded into a rinsing section 1404 filled with distilled water containing a rust preventive via the lifting mechanism 1412. In this case as well, the rinsing section 1404 is deaerated in advance by a second deaerating section 1410. When the barrel 1401 is loaded into the rinsing section 1404, the rinsing section 1404 operates in the same manner as the cleaning section 1403. Subsequently, the objects 1402 are cleaned with hot water in a hot-water cleaning section 1405, and dried by a hot air blower 1408 in a drying section 1406. Thereafter, the objects 1402 are conveyed in a storing section.
The states of objects before and after degreasing processes in such conventional techniques will be compared by using graphs. FIG. 12 shows the absorbance of fats and oils adhering to objects to be processed before a degreasing process in a conventional apparatus using no ultrasonic waves. This absorbance is based on C--H (carbon-hydrogen) stretching vibration in infrared spectrophotometry. FIG. 13 shows the absorbance of fats and oils before a degreasing process in a combination of conventional techniques, such as the one shown in FIG. 11, i.e., a degreasing apparatus which uses an ultrasonic oscillator having an deaerating unit and has a barrel swinging means in addition to a barrel rotating means. FIG. 14 shows the absorbance of fats and oils adhering to the objects after a degreasing process in the case shown in FIG. 12. The absorbance in FIG. 14 decreases to about 42% (0.0710/0.1664) of that in FIG. 12. FIG. 15 shows the absorbance of the fats and oils adhering to the objects after a degreasing process in the case shown in FIG. 13. The absorbance in FIG. 15 decreases to about 36% (0.0543/0.1479) of that in FIG. 13.
In the above conventional degreasing apparatuses using ultrasonic waves, each of techniques (1), (2), and (3) uses only some of the techniques of improving the degreasing efficiency by using ultrasonic waves. In addition, attention is only paid to the characteristics of ultrasonic waves which apply impacts on objects to be processed so as to physically degrease the objects, but no attention is paid to the temperature characteristics of fats and oils adhering to the surfaces of the objects. That is, the conventional apparatuses do not fully enhance the degreasing ability.
With regards to the techniques of hydro-extracting process solutions, technique (4) is not essentially a hydro-extraction method. In addition, as a hydro-extraction process is repeated, the concentration of a solution decreases. The amount of process solution increases or decreases unless the amount of solution carried away is equal to the amount of cleaning solution. Furthermore, with a decrease in the concentration of a process solution, the concentration of the main component in the process solution must be analyzed and tested, and the concentration of the solution must be adjusted. Along with these operations, the costs of chemicals and waste water treatment increase.
Technique (5) is designed to perform hydro-extraction by a free fall and increase the hydro-extraction amount by increasing the length of the time a barrel is held above a bath. There is a limit to hydro-extraction of a process solution impregnating between objects to be processed or between a barrel and objects to be processed while the barrel is at rest. That is, sufficient hydro-extraction cannot be expected.
The conventional apparatus described with reference to FIG. 11 uses water as a process solution, ultrasonic vibrations, deaeration, rotation of the barrel, and the like. That is, this apparatus is a degreasing apparatus which satisfies considerably ideal conditions. However, in the apparatus, since distilled water as a process solution is not heated, the viscosity of fats and oils on the surfaces of objects to be processed does not decrease, and perfect degreasing of the objects cannot be expected. In addition, hydro-extraction is not positively performed after a degreasing process in each bath.